She landed on a planet that had been terraformed. When humans came to inhabit it, Mitzi took control over them and forced them to serve her. Ninety years later, the Tenth Doctor and Rose Tyler landed on the planet.
The Doctor confronted her and persuaded her to leave. Mitzi took a trip in the TARDIS and was taken to the Powell Estate. Rose told the Doctor that she had found Mitzi and renamed her Puffin in her past. She lived for another five years under the Tyler family's care. (PROSE: The Cat Came Back)
When the the Ninth Doctor was investigating the Autons, Rose Tyler told him the reason she had a cat flap was that she used to have a cat. (TV: Rose) Rose later remarked she had a cat like the ginger one she befriended in 2012. (TV: Fear Her)